Certified Rhythm Analysis Technician (CRAT) Practice Exam

In the context of electrophysiology and cardiac rhythms, a narrow-complex beat that occurs without a preceding P wave is indicative of its origin in the conduction system. A premature junctional contraction arises from the junctional tissue of the heart, specifically the area around the atrioventricular (AV) node. This type of contraction typically occurs when there is a premature impulse that originates in that junctional area, bypassing the atria and therefore not having a preceding P wave, which is normally produced by atrial depolarization.

This characteristic is crucial in differentiating it from other arrhythmias. For example, in the case of a premature atrial contraction, there would be a visible P wave associated with the ectopic beat, as it originates from the atria. Similarly, first-degree AV block would still have observable P waves related to the heart's sinus rhythm, albeit with a prolonged interval before the related QRS complex occurs. Lastly, premature ventricular contractions lead to a widened QRS complex due to their origin in the ventricles. Therefore, the absence of a P wave and the narrow nature of the QRS complex strongly support the classification of this early beat as a premature junctional contraction.